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https://issues.apache.org/jira/browse/ARROW-3543?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16957884#comment-16957884
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Shannon C Lewis commented on ARROW-3543:
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Just checking in any updates on this?
> [R] Better support for timestamp format and time zones in R
> -----------------------------------------------------------
>
> Key: ARROW-3543
> URL: https://issues.apache.org/jira/browse/ARROW-3543
> Project: Apache Arrow
> Issue Type: Bug
> Components: R
> Reporter: Olaf
> Priority: Major
> Fix For: 1.0.0
>
>
> See below for original description and reports. In sum, there is a mismatch
> between how the C++ library and R interpret data without a timezone, and it
> turns out that we're not passing the timezone to R if it is set in Arrow C++
> anyway.
> The [C++ library
> docs|http://arrow.apache.org/docs/cpp/api/datatype.html#_CPPv4N5arrow13TimestampTypeE]
> say "If a timezone-aware field contains a recognized timezone, its values
> may be localized to that locale upon display; the values of timezone-naive
> fields must always be displayed “as is”, with no localization performed on
> them." But R's print default, as well as the parsing default, is the current
> time zone:
> https://stat.ethz.ch/R-manual/R-devel/library/base/html/strptime.html
> The C++ library seems to parse timestamp strings that don't have timezone
> information as if they are UTC, so when you read timezone-naive timestamps
> from Arrow and print them in R, they are shifted to be localized to the
> current timezone. If you print timestamp data from Arrow with
> {{print(timestamp_var, tz="GMT")}} it would look as you expect.
> On further inspection, the [arrow-to-vector code for
> timestamp|https://github.com/apache/arrow/blob/master/r/src/array_to_vector.cpp#L504-L514]
> doesn't seem to consider time zone information even if it does exist. So we
> don't have the means currently in R to display timestamp data faithfully,
> whether or not it is timezone-aware.
> Among the tasks here:
> * Include the timezone attribute in the POSIXct R vector that gets created
> from a timestamp Arrow array
> * Ensure that timezone-naive data from Arrow is printed in R "as is" with no
> localization
> -----
> Original description:
> Hello the dream team,
> Pasting from [https://github.com/wesm/feather/issues/351]
> Thanks for this wonderful package. I was playing with feather and some
> timestamps and I noticed some dangerous behavior. Maybe it is a bug.
> Consider this
>
> {code:java}
> import pandas as pd
> import feather
> import numpy as np
> df = pd.DataFrame(
> {'string_time_utc' : [pd.to_datetime('2018-02-01 14:00:00.531'),
> pd.to_datetime('2018-02-01 14:01:00.456'), pd.to_datetime('2018-03-05
> 14:01:02.200')]}
> )
> df['timestamp_est'] =
> pd.to_datetime(df.string_time_utc).dt.tz_localize('UTC').dt.tz_convert('US/Eastern').dt.tz_localize(None)
> df
> Out[17]:
> string_time_utc timestamp_est
> 0 2018-02-01 14:00:00.531 2018-02-01 09:00:00.531
> 1 2018-02-01 14:01:00.456 2018-02-01 09:01:00.456
> 2 2018-03-05 14:01:02.200 2018-03-05 09:01:02.200
> {code}
> Here I create the corresponding `EST` timestamp of my original timestamps (in
> `UTC` time).
> Now saving the dataframe to `csv` or to `feather` will generate two
> completely different results.
>
> {code:java}
> df.to_csv('P://testing.csv')
> df.to_feather('P://testing.feather')
> {code}
> Switching to R.
> Using the good old `csv` gives me something a bit annoying, but expected. R
> thinks my timezone is `UTC` by default, and wrongly attached this timezone to
> `timestamp_est`. No big deal, I can always use `with_tz` or even better:
> import as character and process as timestamp while in R.
>
> {code:java}
> > dataframe <- read_csv('P://testing.csv')
> Parsed with column specification:
> cols(
> X1 = col_integer(),
> string_time_utc = col_datetime(format = ""),
> timestamp_est = col_datetime(format = "")
> )
> Warning message:
> Missing column names filled in: 'X1' [1]
> >
> > dataframe %>% mutate(mytimezone = tz(timestamp_est))
> A tibble: 3 x 4
> X1 string_time_utc timestamp_est
> <int> <dttm> <dttm>
> 1 0 2018-02-01 14:00:00.530 2018-02-01 09:00:00.530
> 2 1 2018-02-01 14:01:00.456 2018-02-01 09:01:00.456
> 3 2 2018-03-05 14:01:02.200 2018-03-05 09:01:02.200
> mytimezone
> <chr>
> 1 UTC
> 2 UTC
> 3 UTC {code}
> {code:java}
> #Now look at what happens with feather:
>
> > dataframe <- read_feather('P://testing.feather')
> >
> > dataframe %>% mutate(mytimezone = tz(timestamp_est))
> A tibble: 3 x 3
> string_time_utc timestamp_est mytimezone
> <dttm> <dttm> <chr>
> 1 2018-02-01 09:00:00.531 2018-02-01 04:00:00.531 ""
> 2 2018-02-01 09:01:00.456 2018-02-01 04:01:00.456 ""
> 3 2018-03-05 09:01:02.200 2018-03-05 04:01:02.200 "" {code}
> My timestamps have been converted!!! pure insanity.
> Am I missing something here?
> Thanks!!
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